Watershedding on surfaces, such as automobile or aircraft windshields, affects the ability of the driver or pilot to see during operation under inclement conditions. A common way to increase the watershed capability of a surface is by applying a hydrophobic surface treatment that lowers the surface energy of the windshield, thereby inducing water to bead up on the windshield surface and roll off. Various types of surface treatments, such as waxes, hydrophobic silicone polymers (e.g., RAIN-X® water repellent) or superhydrophobic coatings with very high contact angles and extremely low roll off angles have been developed to improve the hydrophobicity of glass, metal or polymeric surfaces. However, these known surface treatments are not durable.
U.S. Pat. No. 8,338,351 to Kanagasabapathy et al1 describes a coating composition and process for generating transparent, near-transparent and semi-transparent superhydrophobic coatings on surfaces having a contact angle of greater than 165 degrees that comprise hydrophobic nanoparticles of silsesquioxanes containing adhesion promoter groups and low surface energy groups. 1 The entirety of this and all other publications cited herein is expressly incorporated hereinto by reference.
U.S. Pat. No. 8,187,707 to Van Benthem et at describes a superhydrophobic coating exhibiting a contact angle of greater than 140 degrees comprising raspberry shaped particles comprising primary particles and secondary particles adhering to the surface of the primary particles.
U.S. Pat. No. 6,340,502 to Azzopardi et at describes a composition for a hydrophobic/oleophobic coating containing an alkoxysilane and a halosilane each having a perfluorinated group at least at one end of the molecule and a method for applying the coating to a transparent substrate.
Examples of agents that are known to impart hydrophobic/oleophobic property are fluorinated alkylsilanes as described in EP 0 492 417, EP 0 492 545 and EP 0 672 779. According to these publications, the hydrophobic layer is obtained from a solution containing fluorinated organosilanes (alkyl-trilaho- or trialkoxysilanes whose alkyl group includes at least one end group that is perfluorinated) in a non-aqueous organic solvent is applied to the surface of a substrate. One of the problems associated with these coatings is that of the coating's durability and erosion resistance, as evidenced by the progressive removal of these coatings, particularly by the action of a car's windshield wiper which makes reapplication of the hydrophobic coating necessary.
U.S. Pat. No. 6,072,018 to Wilkes et al describes the formation of abrasion resistant inorganic/organic hybrid material formed by sol-gel condensation of at least one metal alkoxide and a low molecular silane-functionalized organic compound such as a di- or tri-amine, an aliphatic diol, an aromatic diol or a triol. The disclosed materials according to this publication functionalize a low molecular weight compound with an isocyanate-functionalized silane and are reported to be abrasion resistant but not hydrophobic.
There remains a need in the art for transparent hydrophobic coatings to improve the watershed capabilities of glass, polymeric and metallic substrates that are durable in abrasive or aggressive environments, such as after exposure to acids, bases or organic solvents, rain or ultraviolet light. These needed coatings would be useful in numerous applications including as transparent protective coatings for windshields, solar panels, paints, electronics, and the like. It is towards providing such needed coatings that the embodiments of the present invention disclosed herein are directed.